Dental caries is the single most prevalent chronic disease of childhood. Early childhood caries (ECC), a particularly severe form of caries, affects infants, toddlers and preschool children younger than 6 years. Among the general U.S. population, the prevalence of ECC is 25% among children 2-5 years (NHANES III). More recently, NHANES data from 1999-2002 found that the prevalence of caries in young children had increased from the 1988-94 time period, from 24% to 28% in 2- to 5-year-old children (Beltran-Aguilar, et al, 2005). As in the previous surveys, the 1999-2002 NHANES data revealed demonstrated profound disparities in Dental caries prevalence and severity based on race/ethnicity and poverty status. Among American Indian and Alaska Native (AI/AN) children, however, the disease burden is much higher, with 79% of 2-5 year old AI/AN children having ECC (IHS, 2001). The reason for this disparity is not understood, partially because a comprehensive study on the etiology of ECC in this high-risk population has not been undertaken. Until the etiology of the disease is fully understood, there is little hope of developing effective preventive strategies. The overall goal of this study is to identify risk factors for ECC among AI/AN infants and toddlers and to determine if Streptococcus mutans (SM) alone, or in combination with environmental and behavioral factors, increases risk of caries in Native American children. The Specific Aims are: 1) To determine the temporality and fidelity of transmission of Streptococcus mutans in Native American children, 2) To characterize expression of virulence determinants of specific clones of Streptococcus mutans, 3) To determine the composition of total cultivable flora, total Streptococcus mutans and total acid flora in plaque samples of Native American subjects over time, 4) To determine the incidence of ECC in Native American children through age 36 months, and 5) To identify dietary and nutritional risk factors for acquisition of virulent SM clones and ECC in Native American infants and toddlers. Working closely with the Health Board of the Aberdeen Area Tribal Chairman, we will work with the Oglala Sioux tribal community at Pine Ridge, South Dakota from which we will recruit 200 Native mother/child dyads within 1 month of delivery. Information on potential risk factors and caries status will be collected every 4 months until the child is 36 months. As part of our effort to train AI/AN researchers, we will hire a local program coordinator and Dental hygienists. We believe that this assessment of vertical transmission of specific SM clones using DNA fingerprinting approaches will provide valuable information on the acquisition of these cariogenic bacteria in these Native American children.